Digital to analog conversion circuits (DAC) with pulse-width modulated (PWM) outputs are common, but have not used subcycle precision timers to generate pulse width variations, and generally require extensive output filtering. As a result, output resolutions are limited to the highest frequency digital clock rates and counter speeds possible in a given technology. Where the technology permits high-speed docks, high power consumption and excessive heat generation result.
A commonly used method for generating PWM output is through the use of a standard DAC for analog generation. The resulting analog signal is then converted to PWM using analog modulation circuitry. This technique suffers from a lack of accuracy and controllability, and requires additional circuitry.
Delta-Sigma DAC circuits and over-sampling techniques use filtering to reduce undesired output noise. Delta-Sigma DACs use low-resolution high-speed DACs to create high-resolution lower speed outputs using interpolation techniques. By example, a 4 MHZ over-sampling rate might be used for 44 KHz audio. Sample values would be digitally interpolated prior to using a 1-bit DAC. The over-sampled pulse-position signal would be low-pass filtered, leaving only the desired output waveform. Such filtering processes take substantial amounts of time and require extensive additional circuitry. Phase distortion is introduced by these techniques, thus further deteriorating the quality of the output signals.